This invention relates to alkaline cells having means to detect the cell life thereof.
In general, alkaline cells, such as nickel-zinc cells, air-zinc cells, iron-nickel cells, alkali-manganess cells, mercury oxide cells, silver oxide cells, divalent silver oxide cells and the like, maintain continuously their discharge voltage at certain constant values from the beginning to the end stage of discharge.
Accordingly, it has been very difficult to determine in advance when the active material in such conventional alkaline cells is near consumption, and to find out the suitable replacing time of such cells. So that if they are incorporated in very important apparatus, such as a power source of an artificial cardio-stimulating device which directly affects human life, there is a serious disadvantage that such cells must be replaced after a certain definite period of use from a view-point of safety even though the cell active material thereof still remains usable afterward.
It is therefor, an object of this invention to provide an alkaline cell which can detect the end of the cell life by showing a low discharge voltage of indium after the consumption of the main anode active material, that is, zinc.
Heretofore, the use of an anode active material comprising zinc and indium was well-known in the art. The purpose for using this type anode active material is to obtain elimination of mercury, accordingly the zinc particles are treated into solution with the indium or the indium compound is dissolved in hydrochloric acid and washed with much water. And also known in the prior art is an anode active material comprising zinc, indium and mercury. The purpose for using this type active material is to prevent mercury-pollution according to a decrease of the mercury content by adding a micro-quantity on the order of 0.0001-2% of indium by weight of the anode active material.
Further, the anode active material comprising zinc-alloy containing 0.5% of lead (Pb), 0.02% of cadmium (Cd) and 0.02% of indium (In) by weight is also well-known in the art.
Furthermore, the anode active material comprising indium only is well-known. For example the indium-mercury oxide: (In/HgO) Cell (open circuit voltage Eo=1.16 V) and the indium-monovalent silver oxide (In/Ag.sub.2 O) cell (open circuit voltage Eo=1.35 V) have heretofore been produced.
However, although indium is an excellent anode active material as is zinc, it is a very rare material as a natural resource and high in price, so that such cells have not been widely developed.
As mentioned above, the indium anode active material and the zinc anode active material containing one of indium and mercury, or both, are well-known in the art, but the objects of these conventional cells are largely different from that of this invention. And the indium content of conventional cells is very small in quantity, on the order of 0.0001-2% by weight, however, the object of this invention does not aim to decrease the mercury content of the zinc anode active material but to produce indium-mono silver oxide potential (Eo=1.35 V) at the end stage of the cell by adding over 2% of indium for zinc by weight and utilizing the indium as an active material of the cell. And moreover, the main anode active material of the cell of this invention is zinc, therefore the raw material cost of the cell does not become so high.
According to this invention, when the cell approaches the end of its useful life, such can be detected by altering the cell discharging voltage at the end discharging stage so as to be able to replace it with a new one before the cell drops its discharge voltage to stop operations of electronic instruments such as electronic wrist watch, camera, pocket-bell, hearing aid, artificial cardio stimulating device and the like.